Residue‐Free Droplet Transport Against Gravity via Wettability‐Patterned Liquid‐Like Surfaces

Abstract

AbstractLifting individual water droplets against gravity without external energy input is reported. Classical capillary rise requires the complete wetting of a transport pathway, resulting in water loss and poor collection efficiency. Boosting Laplace pressure propulsion while diminishing contact line pinning enables lossless water droplet ascension. Surfaces with properly designed physicochemical gradients can propel single water droplets as high as 65 mm against gravity, enabled by 1) surface wettability patterns, 2) liquid‐like polymer brushes, and 3) controlling droplet size within a shorebird beak‐inspired wedge geometry. Surface wettability patterns induce droplet elongation toward the gap‐to‐apex direction of the wedge geometry, which boosts Laplace pressure propulsion by increasing droplet length and diminishes contact line pinning by decreasing droplet width. Polymer brushes for wettability patterning exhibit minimal contact angle hysteresis, minimizing contact line pinning and enabling residue‐free droplet ascension. Controlling the droplet size prevents the dominance of either contact line pinning or gravity over Laplace pressure propulsion, enabling droplet transport against gravity. Utilizing these design rules, low surface tension n‐decane is also transported against gravity, and a particle‐laden solution is separated using sedimentation and against‐gravity transportation. Such surfaces may facilitate lossless, against‐gravity, and power‐free water pumps in numerous emerging sustainability and energy applications.